1. Field of the Invention
The present invention relates to a method for storing video frame data in a memory of a video apparatus and, more particularly, to a video frame data storing method which can reduce the amount of memory required in a video apparatus.
2. Discussion of the Related Art
Generally, video frame data is composed and displayed on a screen in units of pixels. For effective transmission and storage of the video frame data, it is initially encoded. Since the video frame data contains an enormous amount of information, a video compression technique is used during encoding. The video compression technique is implemented by eliminating video information that is repeated between spatial and temporal domains or by coding the video information to a constant form. As one of the most widely known video compression techniques, there is the MPEG (Moving Picture Expert Group) specification.
The MPEG specification initially encodes the video frame data by a unit of a macro block and decodes the encoded video frame data by a unit of the macro block for the purpose of storage and display. Each macro block consists of 16xc3x9716 pixels, i.e., 16 scanning lines. The MPEG specification has recently been adopted for the high quality of an image in systems such as digital TV, direct broadcasting satellite (DBS), DVD, and high definition television (HDTV).
In an NTSC broadcasting system, one frame of data includes 480 scanning lines each having 720 pixels, as shown in FIG. 1a. A moving picture is achieved by displaying about 30 frames of data per second.
In a PAL broadcasting system, one frame of data consists of 576 scanning lines each having 720 pixels, as shown in FIG. 1b. The moving picture is formed by displaying about 25 frames of data per second.
Typically, one frame of video data is divided into an odd field (or a top field) and an even field (or a bottom field), and displayed on the screen in the order of the odd field and then the even field. In the following description, the odd and even fields may be referred to as first and second fields without distinguishing them. Moreover, one video frame of data is divided into an upper part and a lower part. In the NTSC system, the upper part and the lower part each have 240 scanning lines, respectively. Since the NTSC system uses an interlaced scanning method, one scanning line of the odd field and one scanning line of the even field are alternatively displayed on the screen, as indicated in FIG. 2. Therefore, in the frame data of the NTSC system, the upper part and the lower part, respectively, have 120 scanning lines of the odd field and 120 scanning lines of the even field.
FIG. 3a is a schematic block diagram showing a typical decoding part of a video apparatus, such as a television receiver and a video cassette recorder. A conventional method for storing the video frame data in a memory will now be described with reference to FIG. 3a. 
A decoder 20 sequentially decodes encoded video frame data in response to a control signal CS1 of a controller 10. A memory 30 sequentially stores the video frame data generated from the decoder 20 by a unit of the frame data in response to another control signal CS2 of the controller 10 and then supplies the stored frame data to another storage device 50 or a display unit 40, for example, a television receiver or a monitor. That is, each video frame data is supplied to the display unit 40 or the storage device 50 after it is completely stored in the memory 20.
In more detail, each video frame of data consists of an odd field and an even field. As shown in FIG. 3b, the odd field data of the video frame data generated from the decoder 20 is stored in a first region 30a of the memory 30, and the even field data thereof is stored in a second region 30b of the memory 30, as shown in FIG. 3b. In this case, each field data is sequentially stored in each region by a unit of a constant number of scanning lines (8 or 16 scanning lines, for example). Thus, if one frame of data is divided into the odd field data and the even field data, and if these field data are stored in the first and second regions 30a and 30b, the memory 30 supplies the odd field data stored in the first region 30a to the storage device 50 or the display unit 40 in response to the control signal CS2 of the controller 10 in a stored order of 1a, 2a, 3a , . . . (nxe2x88x921)a, na. Thereafter, the memory 30 supplies the even field data stored in the second region 30b to the display unit 40 or the storage device 50 in a stored order of 1b, 2b, 3b , . . . (nxe2x88x921)b, nb. The next video frame of data generated from the decoder 20 is then stored in the memory 30 in the same way as the above-described processes and then applied to the display unit 40 or the storage device 50.
It should be noted that each video frame of data is supplied to the display unit to be displayed or to another storage device to be stored after it is completely stored in the memory. Therefore, the memory 30 must have a capacity which is capable of storing a full frame of video data. However, there are disadvantages which will hereinafter be described. The memory is typically fabricated by a manufacturing company to a multiple of 2, that is, 1, 2, 4, or 8 megabytes (MB), etc. Hence, the maximum capacity of the video frame data to be stored does not accurately coincide with the capacity of commercially available memories. For example, in order to store the video frame data of the MPEG specification according to the PAL system, a memory capacity of a maximum of 1,866,240 bytes is needed. Further, in order to store each video bit stream before decoding, a memory capacity of 229,376 bytes is required. It is necessary to have an additional memory capacity of about 500,000 bytes in order to store on-screen display (OSD) data, audio data, and system data. Consequently, a memory capacity of about 2.6 MB is needed to store the video frame of data of the MPEG specification according to the PAL system during decoding.
However, as previously noted, since a memory having a memory capacity of 2.6 MB is not typically commercially fabricated, the next largest commercially available memory, which typically has a capacity of 4 MB, must be selected. Therefore, when designing the decoding part of the video apparatus, there occurs an unnecessary increase in manufacturing cost. Moreover, since the capacity of the video frame data for the PAL system is larger than that for the NTSC system, the video frame data for the PAL system cannot be stored in the memory corresponding to the NTSC system. In other words, the video apparatus of the PAL system is not compatible with that of the NTSC system.
Accordingly, the present invention is directed to a method for storing video frame data in a memory that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for storing video frame data in a memory which can reduce the capacity of a memory used in a decoding part of a video apparatus.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method for storing video frame data in a memory includes the steps of: sequentially receiving the video frame data; dividing the video frame data into a first part and a second part; storing the first part in the memory; and storing the second part in the memory while the stored first part is read from the memory for a certain purpose; and reading the second part stored in the memory for the certain purpose.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.